1. Field of the Invention
The present invention relates to a developing device that develops an electrostatic latent image by use of a nonmagnetic one-component developing agent in image forming devices such as an electrographic device, printer and so forth.
2. Description of the Related Art
Along with the spread of image forming devices such as electro photographic color printers, color multifunction peripherals (MFP) and so forth, used a developing device that develops an electrostatic latent image by use of toner as a non-magnetic one-component developing agent, since it enables to obtain high quality images without concentration control, and enables users to easily exchange developing devices and toners with excellent user maintenance properties, and further enables to make a simplified and compact and light weight device without necessity of magnetic materials.
So as to obtain preferable developed images by use of this non-magnetic one-component developing agent, it is required to charge toner preferably and to form a thin and uniform toner layer on a developing roller. For this reason, in the prior art, developing devices that press contact a layer regulating blade on a developing roller for forming a toner layer are disclosed in Japan Patent Disclosure (Kokai) No. 5-241432 and Japan Patent Disclosure (Kokai) No. 8-240987. However, in the developing rollers disclosed in the above, the surface of each developing roller is made of conductive rubber.
In such a developing device employing a developing roller made of conductive rubber, it is possible to attain preferable images in a color image forming device whose process speed is relatively low, for example 100 mm/s or so, on the other hand, when employed in a color image forming device whose process speed is over, for example 180 mm/s, space between a layer regulating blade and a developing roller will be made wider owing to pressure from a toner layer that is formed around the developing roller. Accordingly, it is not possible to sufficiently regulate a toner layer into a uniform and thin layer, as a result, toner will drop down from a developing device, which has been inconvenient.
On the other hand, also in the prior art, employed for these years is a full color image forming device wherein a photosensitive belt is used in the place of a photosensitive drum, and thereby an electrostatic latent image is formed on this photosensitive belt. In this type of image forming device, an electrostatic latent image that is formed on a photosensitive belt is temporarily transferred onto an intermediate transfer medium, and toners are placed thereon on the intermediate transfer medium to attain a full color image. And as a developing device for supplying toners to such a photosensitive belt, one whose developing roller surface is made of metal has been developed. This metallic developing roller, in comparison with a conductive rubber roller, can make narrow a nip width with a layer regulating blade, and also make sharp the pressure distribution of such a layer regulating blade to a developing roller, therefore, it is suitable for high speed operation.
Namely in more concrete manners, as shown in FIG. 1, a layer regulating blade 2 wherein an urethane rubber sheet 2b of thickness about 1 mm is adhered to a stainless steel plate spring 2a, is pressed onto a developing roller 1 whose surface is made of aluminum (Al), thereby a toner layer is formed even on the surface of the developing roller 1.
However, even though the surface of the developing roller 1 is made of metal, when a process speed is made higher, the regulation of toner layer by the layer regulating blade 2 to the developing roller 1 will become insufficient, causing toner spilling. On the other hand, if the pressing force of the layer regulating blade 2 to the developing roller 1 is strengthened so as to prevent toner spilling, the driving torque of the developing roller 1 will become large, causing toner to fix onto the developing roller 1 or the layer regulating blade 2, and leading to image failure.
Therefore, in order to be able to regulate a toner layer without increasing pressing force, by making a layer regulating blade as well as a developing roller into a metallic plate spring, making narrower the nip between the developing roller and layer regulating blade, we have tried making sharper the pressure distribution of layer regulating blade to developing roller. As a result, since a metallic developing roller and layer regulating blade directly contact each other, both of them are scratched, consequently, streak failures are made on images, therefore, we have not yet seen its practical application so far.
As a consequence, in a high speed image forming device, there is a demand for attaining preferred developed images, by forming a thin and uniform layer of toner as a non-magnetic one-component developing agent on a developing roller surface, without damaging both a developing roller and a layer regulating blade, and without deteriorating display quality by dirty images caused by dirt on peripherals by toner spilling or toner attachment onto a developing roller or a layer regulating blade.
Accordingly, the object of the present invention is to provide a developing device that may supply a thin and uniform layer of toner as a non-magnetic one-component developing agent to a developing roller, without deteriorating display quality owing to toner spilling over peripherals or toner attachment onto a developing roller or a layer regulating blade, and may be applied to a high speed image forming device.
It is another object of the present invention to provide a developing device that prevent a developing roller and/or a layer regulating blade from being damaged when toner as a non-magnetic one-component developing agent is applied thin and uniform onto the surface of developing roller, and may be applied to a high speed image forming device.
According to the present invention, there is provided a developing device comprising developing agent supplying means shaped a roller for supplying developing agent onto an electrostatic latent image on an image carrier; layer regulating means pressure contacting with the developing agent supplying means for regulating uniformly a layer thickness of the developing agent that is supplied to the developing agent supplying means; and an elastic resin coat layer coated on the surface of the layer regulating means, wherein the thickness t of the elastic resin is 10xc3x97axe2x89xa6txe2x89xa6300 [xcexcm] when the surface of the developing agent supplying means is formed of a metallic material whose surface roughness Rz is a [xcexcm], and the layer regulating means is made of a metallic material.
Further according to the present invention there is provided a developing device comprising a developing roller configured to supply developing agent onto an electrostatic latent image on an image carrier; a layer regulating blade pressure contacting with the developing roller to regulate uniformly a layer thickness of the developing agent that is supplied to the developing roller; and an elastic resin coat layer coated on the surface of the layer regulating blade, wherein the thickness t of the elastic resin is 10xc3x97axe2x89xa6t less than 300 [xcexcm] when the surface of the developing roller is formed of a metallic material whose surface roughness Rz is a [xcexcm], and the layer regulating blade is made of a metallic material.
Still further, according to the present invention, there is provided a developing device comprising a developing roller configured to supply developing agent onto an electrostatic latent image on an image carrier; and a layer regulating blade pressure contacting with the developing roller to regulate uniformly a layer thickness of the developing agent that is supplied to the developing roller; wherein the surface of the developing roller is made of brass, and the layer regulating blade is formed of stainless steel, and the pressing force of the layer regulating blade to the developing roller is 70-100[gf/cm].